The present disclosure relates to improvements to thermodynamic devices that approximate the Ericsson cycle, Brayton cycle, or regenerated Brayton cycle. These cycles and various ways of implementing them are known in the art. They can operate as engines or refrigerators. The Ericsson cycle is attractive since it can theoretically operate at the Carnot efficiency, which is the maximum possible efficiency for a heat engine or refrigerator.
Brayton cycle devices, such as gas turbine engines and Brayton cycle cryocoolers have achieved widespread commercial use. However, Ericsson cycle devices have not achieved widespread commercial success. A principal difficulty of implementing a practical device that operates in a manner substantially similar to the Ericsson cycle is the requirement for isothermal or near isothermal compression and expansion of the working fluid. When a gas is compressed, the temperature of the gas increases. To keep the temperature of the gas constant during compression, the gas must be cooled while it is compressed. In practice, isothermal compression of a gas is extremely difficult to achieve because, for practical compression machines, the area available for heat transfer is very small and the compression process occurs very quickly. A compressor could be made with a large heat transfer area and a very slow compression process. This, however, would typically result in a large and expensive device that was not commercially practical.
The situation is similar for the expansion process where the temperature of the gas decreases as it expands and it is typically not practical to add a significant amount of heat to the gas during the expansion process. In lieu of heating and cooling the gas during the expansion and compression processes, respectively, external heat exchangers can be used for adding and rejecting heat to the system. This arrangement results in a Brayton cycle device.
A combination of heat addition external to the expansion and compression process and during the expansion and compression process results in a cycle that has Ericsson cycle and regenerated Brayton cycle characteristics. Here this type of hybrid cycle will be referred to as an Ericsson cycle for convenience.
Various schemes have been devised to overcome the challenge of effective heat addition during the expansion processes and heat rejection during the compression process. Y. A. M. Elgendy drafted the study titled ANALYTICAL DETERMINATION FOR THE PERFORMANCE OF A NEW POWER GENERATION TECHNOLOGY and proposed using a scroll compressor and expander in an Ericsson cycle arrangement. This disclosure is expressly incorporated herein by reference. Scroll machinery has a relatively large surface area available for heat transfer compared with other technologies such as reciprocating compressors or turbomachinery. Elgendy also proposed using heat pipes or other means to increase the rate of heat transfer. Kim et al. disclosed in U.S. Pat. No. 7,124,585 (expressly incorporated herein by reference) a similar Ericsson cycle arrangement with scroll machinery. Corey (U.S. Pat. No. 4,984,432) and Hugenroth et al. (U.S. Pat. No. 7,401,475) (both of which are expressly incorporated herein by reference) disclosed methods of using liquid flooding during the compression and expansion processes to approach isothermal compression and expansion. Hugenroth et al. used scroll or screw machinery due to their ability to tolerate liquid flooding.